Forced induction 100cc

[DEATH_INC.]

How the hell did I miss this thread????
Looking pretty awesome fella!

All this supercharging talk.....I remember years ago a guy made a KX500 engine (I think) with a four stroke head on it....used the bottom end compression to supercharge the top end. Had Valves like a four stroke, but fired every stroke like a two stroke. Went well apparently, but ran a bit hot. Long time ago...don't know if there's anything on the net about it....

[Drew]

Yo Glen, if you haven't mounted the supercharger yet, why don't you just get an electric start set of casings for the motor. Viola, drive without hacking cases to bits.

[Drew]

How the hell did I miss this thread????

You're not as young as you were bro.

[Sketchy_Racer]

Yo Glen, if you haven't mounted the supercharger yet, why don't you just get an electric start set of casings for the motor. Viola, drive without hacking cases to bits.

Thought of that, but makes it to difficult to change pulley sizes and given that it is going to be incredibly hard for me to calculate the efficiency of the supercharger it is really going to be a hit and miss with the pulley ratios.

Drive really isn't an issue and the charger is all mounted up now so were getting close to business time.

[Sketchy_Racer]

So this evening I have been doing some research into some ideas to combat the pulsing effect from supercharging a single cylinder engine. I have stumbled upon a tech article from SAE site so thought it would be worth the download.

I would like to share it but it is secured PDF so wont be much use to you all but the short of the long is that they took a 660cc yamaha quad bike engine and supercharged it, despite all the cons against it. The motor is for the formula SAE racecar which is designed and built by university students, such as the one early linked in this thread.

There is some very complex (well, complex to me) calculations and algorithms that they have used to derive the data that they needed to create there intake system, but the concepts are what excited me.

The general rule of thumb is that with a supercharged single cylinder motors that plenum size is very important in dealing with the pulses caused by the 180 degree intake cycle. So a large plenum is used to act a fluid (air is defined as a fluid) cushion for these pulses as well as acting as a pneumatic accumulator. The way it works is that the supercharge is displacing a fixed volume of air, however the motor is drawing it in as gulps taking a gulp for 180 degrees of crank rotation ever second rotation of the crank. So if we did not have a plenum what would happen would when the intake valve opens it would take a big gulp of air from the supercharger, but then the intake valve shuts abruptly causing a massive pressure spike. The supercharge is now trying to force all that air into a volume and the pressure spike would go through the roof causing massive surging and all sorts of issues.

So a large plenum is the solution to this, but it comes with a major down fall, that is being that it creates a lag between on and off throttle application as it takes time for the supercharger to build the pressure inside this large volume tank.

In this SAE paper they have used a very simple concept to achieve the best of both worlds using a classic helmholtz resonator to give work with the frequency of the intake pulses and the supercharge flow. The only down side being that it only works in certain RPM ranges where the frequency is correct.

Here some screen shots from the article (shhs don't tell them)



Another option I was looking into was to install a reed valve on the intake to the plenum so that when the throttle is shut and the intake vacuum opens the blow off valve the pressure built inside the plenum remains as well as any back pulses are contained meaning that surge is taken care of. These are two items I am going to research some more. But the reed valve solution intrigues me

So still learning plenty and so far happy that I have not had to back track too much so hopefully with enough research I wont have to re-do much of the work when it comes time to run the bike.

Here are some pictures of the supercharger mount, really simply desing works really well and is amazingly rigid which is very important. I have gone with using steel for the mounting structures for the engine and supercharger as my experience is that anything fabricated from ally cracks in these applications unless is really thick, thus weighing the same as the steel one!



It still needs a tidy up and a paint job.

[Drew]

Why not mount the carb inside the plenum mounted as normal. Lag is no longer a problem, and you wont need to keep replacing blower rotors from being eaten.

[Sketchy_Racer]

Why not mount the carb inside the plenum mounted as normal. Lag is no longer a problem, and you wont need to keep replacing blower rotors from being eaten.

Haha because it's going to be running EFI with a throttle body

[Grumph]

Interesting stuff,but IMO, for your layout a blind alley...
You as I understand it, are going to blow air into a plenum and then through the throttle/injection body into the port. IMO again, you won't have any lag problems with that layout.
The blowoff valve is going to take care of pressure spikes when the throttle is closed and pressure in the plenum will remain at whatever the base setting is on the blowoff valve. No reed valves needed, when it's turning the blower is a very effective one way valve....

Mounts...I did a 10mm alloy plate up the side of our motor which the end of the blower mounted to. Absorbed all the drive stresses and located the blower laterally. I had no room to move the blower once in so there was a jockey tensioner on the plate also. The plate was also a convenient place to mount ignition pickups...trigger on the backside of the drive pulley. And a seal in the plate where the crank came through.

[ducatilover]

Haha because it's going to be running EFI with a throttle body

What's the EFi set up off?
I have to agree with Grumph on the blow off valve issue, they're simple, effective and generally reliable.

[Drew]

What's the EFi set up off?
I have to agree with Grumph on the blow off valve issue, they're simple, effective and generally reliable.

Don't be so lazy, read the thread.

He linked to it earlier but I forgot.

Anyhoo, carb or throttle body, mount it at the engine intake and the lag problem is a non issue.

[jonbuoy]

The Eatons come with a backfire valve (just a round spring loaded cap) in the plenum and a vacuum bypass valve that means the engine is only under boost when the engine needs boost you probably not too worried about idle surge or fuel economy on a race bike. Risk of derailing the thread but there is some nice examples of supercharged singles on here:

http://www.elsberg-tuning.dk/supercharging.html#smog

[DEATH_INC.]

That setup reminds me of the old 'boost bottles' that the yammie mxers ran in the early 80's
If ya do what drew sez, run the tb/carb in the normal position, then you make a recirculation system/bov to feed excessive boost back into the charger intake (or vent it...whatever) the plenum will stay at max boost levels with the throttle closed, and be right there ready to go when you crack it back on....
There's no fuel at that point either so no worries about that.
edit: Doh! Pretty much what grumph is saying...

[Sketchy_Racer]

Interesting stuff,but IMO, for your layout a blind alley...
You as I understand it, are going to blow air into a plenum and then through the throttle/injection body into the port. IMO again, you won't have any lag problems with that layout.
The blowoff valve is going to take care of pressure spikes when the throttle is closed and pressure in the plenum will remain at whatever the base setting is on the blowoff valve. No reed valves needed, when it's turning the blower is a very effective one way valve....

Mounts...I did a 10mm alloy plate up the side of our motor which the end of the blower mounted to. Absorbed all the drive stresses and located the blower laterally. I had no room to move the blower once in so there was a jockey tensioner on the plate also. The plate was also a convenient place to mount ignition pickups...trigger on the backside of the drive pulley. And a seal in the plate where the crank came through.

Yes having the throttle body placed on the intake to the motor is certainly going to control a lot of the lag issue, but it still wont overcome the issues with the large pressure waves caused by the intake. I am going to start simple as I like the KISS theory but I will keep these options in mind for future issues/optimisation options.

I'm lucky with the design on the pitbike engine that the flywheel compartment is completely sealed by the ignition back plate making is even easier to get the drive from the motor. I am probably still going to add some gussets in the supercharger mount just to add a little bit more rigidity.

What thickness belt would you recommend? I was thinking of something along the lines of 15mm poly vee belt

What's the EFi set up off?
I have to agree with Grumph on the blow off valve issue, they're simple, effective and generally reliable.

I have ordered a kit from this site - http://www.ecotrons.com

They give you a few kit options, I have got the one that is for turbo applications which also gives me ignition control.

The Eatons come with a backfire valve (just a round spring loaded cap) in the plenum and a vacuum bypass valve that means the engine is only under boost when the engine needs boost you probably not too worried about idle surge or fuel economy on a race bike. Risk of derailing the thread but there is some nice examples of supercharged singles on here:

http://www.elsberg-tuning.dk/supercharging.html#smog

I will certainly be running a blow off valve as I want to minimise engine braking and shutting the throttle on a supercharger at high RPM is going to cause a lot of load on the pulley trying to stop the motor really fast. I have looked at car type ones but they are all only vacuum operated, I want one that is pressure sensitive (like a waste gate) but without the weight of one so I may look at building my own, or modifying a car blow off valve.

I have had a long look through that site, a lot of interesting photos on there. I had a brief email conversation with him about the blowers but haven't heard from him since. He also runs the Helmholtz resonator on his bike, but he is running a draw through system.

That setup reminds me of the old 'boost bottles' that the yammie mxers ran in the early 80's
If ya do what drew sez, run the tb/carb in the normal position, then you make a recirculation system/bov to feed excessive boost back into the charger intake (or vent it...whatever) the plenum will stay at max boost levels with the throttle closed, and be right there ready to go when you crack it back on....
There's no fuel at that point either so no worries about that.
edit: Doh! Pretty much what grumph is saying...

The old boost bottles are exactly that, a resonator. Many cars still have them in the intake system to aid flow at low RPM, and many dumbarse boy racers remove them in favor of their custom "high performance" intake tubes with accompanying pod filter...

[Sketchy_Racer]

So I was bored again last night so I thought I would do a couple more videos, this time of how I go about setting up the CAM software to machine the two lobe rotor.

[Yow Ling]

Hey Glen, could you put a sprag clutch in the supercharger drive, so when the engine decelerates it can let the supercharger coast , rather than force it to decelerate at the engine rate